In modern times, with the ecological concerns about conservation of raw materials and the rapid decline of available landfill space, it has become increasingly desirable to recover and recycle used raw materials. Thus, recovered wastepaper represents a valuable source of raw material for the paper industry. In order for the wastepaper to be regenerated into a viable starting material and to produce a commercially acceptable paper, the wastepaper must be treated to remove any ink particles and non-ink contaminants.
Many prior art processes are known for deinking wastepaper, many of which are directed to the development of deinking agents. Poppel et al., U.S. Pat. No. 4,586,982 describe a process comprising treating the wastepaper in a pulper at an alkaline pH with alkali silicate, an oxidatively active bleaching agent, an acid selected from the group consisting of fatty acids and resinic acids containing more than 10 carbon atoms and a dispersing agent wherein the acid and dispersing agent are employed together in an oil-in-water emulsion. Other disclosures of deinking agents are set forth in, for example, Wood et al., U.S. Pat. No. 4,618,400 (thiol ethoxylate compounds); Wood et al., U.S. Pat. No. 4,561,933 (a mixture of C.sub.8 to C.sub.16 alkanols and alcohol ethoxylates); DeCeuster et al., U.S. Pat. No. 4,343,679 (compounds capable of liberating ions with a positive charge equal or greater than 2); Bridle, U.S. Pat. No. 4,483,742 (pine oil and a soap-making fatty acid); and Tefft, U.S. Pat. No. 4,786,364 (a hydrolyzed copolymer of dimethyldiallyl ammonium chloride and acrylamide).
Other prior art processes are directed to improvements in either washing or flotation methods of separating ink particles from wastepaper fibers.
Nanda et al., U.S. Pat. No. 4,548,673 describe a deinking flotation method comprising the steps of independently introducing air into a fiber stock slurry, mixing the air bubbles and slurry, and separating the ink-laden air bubbles from the fiber slurry, where each of these steps is independently controlled. Shiori et al., U.S. Pat. No. 4,749,473, describe introducing air bubbles into the wastepaper pulp slurry through a number of orifices formed on a peripheral surface of at least one rotatable horizontal cylinder located in the bottom portion of a flotation vessel. Pfalzer et al., U.S. Pat. No. 4,277,328, describe employing an impeller at the bottom of a flotation apparatus for dispersing air into the wastepaper pulp slurry.
None of these processes however are directed to providing a method which facilitates both removal of ink particles and enhanced removal of non-ink contaminants. The presence of non-ink contaminants is a recurring problem in the recycling of wastepaper. These contaminants have in most cases been added intentionally during the actual manufacture of the paper in order to give the fibrous structures special additional properties, or during processing of the paper. The contaminants may be polymeric and are of various types such as polyvinyl acetates, vinyl acetate/ethylene coplymers, waxes, styrene/butadiene latices, polystyrene, hydrocarbon resins, polyisoprenes, resin esters, butyl rubber or polyamides. They end up in specific products such as sealing tapes, adhesives used for bookbinding, coated cardboard, contact adhesives, envelopes and adhesives for gluing cardboard.
The polymeric contaminants, especially glues or adhesives, are especially troublesome. They form agglomerates which deposit in the installations for regenerating wastepaper and in the machines for manufacturing paper or cardboard. Moreover, these agglomerates detract from the final appearance of the sheet of paper or cardboard and they cause tearing when the paper is used as printing paper, in particular in rotary printing machines.
Maloney et al., U.S. Pat. No. 4,643,800 teaches blending contaminated secondary fiber with water, a substituted oxyethylene glycol surfactant and a dispersant and coincidently heating the blend to a temperature above the melting point of the contaminant to be dispersed and removed. Other disclosures of high temperature decontamination include Maloney et al., U.S. Pat. No. 4,483,741 and Maloney, U.S. Pat. No. 4,599,190.
Hageman et al., U.S. Pat. No. 4,548,674 disclose decontaminating wastepaper fibers by pulping the wastepaper in an acidic aqueous solution (pH=2.5 to 6.5) containing at least one peroxide compound selected from among organic and inorganic peracids.
Clement, U.S. Pat. No. 4,780,179 discloses a decontamination method comprising a cold temperature low mechanical energy pulping step, followed by screening, thickening and high temperature high shear washing steps to aid in removal of non-ink contaminants. The Clement patent however suffers from the need of requiring separate steps of non-ink contaminant removal, ink softening and ink particle detachment, each step requiring a specific set of parameters and thus describing an expensive and difficult to accurately control process.
Thus, there remains a long felt need in the art to provide a simple and easy to control wastepaper treatment process whereby there is obtained enhanced removal of both ink particles and non-ink contaminants.